Appetite and Food Intake

Central Control, Second Edition

Ruth Harris

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781498723169
• eBook ISBN: 9781351646482
• Edition: 2
• Topic: Medizin
• Subtopic: Ernährung, Diätetik & Bariatrie

Nearly half of the world's adult population is either clinically obese or overweight. Excess weight increases risk for multiple other chronic diseases and represents a major global health issue. Weight gain results from an imbalance between energy intake and expenditure, which can only be corrected if the physiologic and neuroendocrine systems that have the potential to control energy balance are identified. The first edition of this book reviewed knowledge on the intake of micro- and macronutrients, food choice, and opposing views on whether or not there are mechanisms that control food intake. Appetite and Food Intake: Central Control, Second Edition contains all new chapters and serves as a companion to the first by reviewing current knowledge on neuroendocrine mechanisms that influence food intake and glucose metabolism, including environmental influences on their development, with an emphasis on recent progress in understanding forebrain and hindbrain control of ingestive behavior.In addition, there is a discussion on the benefits derived from novel models for exploring ingestive behavior and the progress that has been achieved due to new technologies. Although major progress is being made in understanding the complex interplay between different control systems, the limits of our knowledge are acknowledged in chapters that review the efficacy of current weight control drugs and the relative importance of fat free mass and body fat in driving food intake.

1Appetite Control in C. elegans

Kristen Davis, Mi Cheong Cheong, Ji Su Park, and Young-Jai You

1.1Introduction

1.1.1Caenorhabditis elegans Feeding

1.1.2C. elegans as a Model to Study Appetite Control

1.2Behaviors and Mechanisms

1.2.1Hunger

1.2.1.1Muscarinic Signal

1.2.1.2Opioid Signal

1.2.2Satiety

1.2.2.1Satiety Quiescence

1.2.2.2The Mechanisms: TGFβ and cGMP Pathways in ASI Neurons Regulate Satiety

1.3Food Preference

1.3.1Quality

1.3.2Familiarity

1.4Conclusions

Acknowledgment

Literature Cited

1.1Introduction

1.1.1Caenorhabditis elegans Feeding

Caenorhabditis elegans is a 1-mm-long free-living nematode that feeds on bacteria. The feeding organ of C. elegans is a pharynx, a neuromuscular tube responsible for sucking bacteria into the worm from outside, concentrating them, and grinding them up (Doncaster 1962, Seymour et al. 1983). The basic mechanics and the neurons and muscles used to execute feeding motion are important for understanding several feeding behaviors and are therefore briefly described. More details regarding cellular and nuclear composition, the structure, electrophysiology, and the molecular components can be found in Avery and You (2012).

The motions of the pharynx are largely regulated by its embedded nervous system. It contains 20 neurons of 14 different types (Albertson and Thomson 1976). Three of these 14 are particularly important for feeding motions: MC, M3, and M4. MC and M3 control the timing of pumping, a full cycle of contraction and relaxation of the pharyngeal muscle (Avery 1993a): MC controls when a contraction starts (Raizen and Avery 1994, Raizen et al. 1995), and M3, when it ends (Avery 1993b, Raizen and Avery 1994). M4 is necessary for the peristaltic movement within the pharynx to transport trapped bacteria to the grinder, where the bacteria are crushed (Avery and Horvitz 1987). The pumping frequency has been shown to be altered by external cues and the neurons outside the pharynx (Greer et al. 2008). However, the exact connections between extrapharyngeal neurons and the pharynx that control feeding rates or motion are not clearly known.

Pharyngeal neurons contain both neuropeptides and small-molecule neurotransmitters. The most important of the small transmitters are acetylcholine, glutamate, and serotonin. Acetylcholine is released from MC to the pharyngeal muscle to initiate the muscle contraction via a nicotinic channel receptor, EAT-2 (Raizen et al. 1995, McKay et al. 2004). Acetylcholine also regulates a hunger response by controlling pharyngeal muscle responsiveness during starvation via a muscarinic receptor GAR-3 (You et al. 2006). GAR-3 is a C. elegans homolog of mammalian M3 muscarinic receptor (Steger and Avery 2004). M3 receptor knockout mice eat less and become skinny, showing conservation in controlling feeding via a similar molecular mechanism (see Section 1.2.1.1). Glutamate is released from M3 to end pharyngeal muscle contraction via an invertebrate-specific glutamate gated chloride channel, AVR-15 (Dent et al. 1997). Serotonin is released from either a neurosecretory-motor neuron (NSM) inside the pharynx or from extrapharyngeal neurons (e.g., ADF) to increase the pumping frequency (Niacaris and Avery 2003, Song et al. 2013). Neuropeptides play important roles, but they are still, for the most part, poorly understood. Recently, Cheong et al. (2015) discovered that one type of neuropeptide homologous to mammalian opioids regulates a hunger response in C. elegans (see Section 1.2.1.2).

1.1.2C. elegans as a Model to Study Appetite Control

Studies from the past 50 years found several fundamental mechanisms of appetite control: specific brain regions integrate signals from the gut, assess the body’s nutritional status, and control feeding. Although it has been well known that the hypothalamus in mammals is t...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright Page
• Contents
• Preface
• Author
• Chapter 1 Appetite Control in C. elegans
• Chapter 2 Central and Peripheral Regulation of Appetite and Food Intake in Drosophila
• Chapter 3 The Hamster as a Model for Human Ingestive Behavior
• Chapter 4 Beyond HomeostasisUnderstanding the Impact of Psychosocial Factors on Appetite Using Nonhuman Primate Models
• Chapter 5 Untangling Appetite Circuits with Optogenetics and Chemogenetics
• Chapter 6 The Use of Functional Magnetic Resonance Imaging in the Study of Appetite and Obesity
• Chapter 7 Development of Hypothalamic Circuits That Control Food Intake and Energy Balance
• Chapter 8 Maternal and Epigenetic Factors That Influence Food Intake and Energy Balance in Offspring
• Chapter 9 Monitoring and Maintenance of Brain Glucose SupplyImportance of Hindbrain Catecholamine Neurons in This Multifaceted Task
• Chapter 10 Hindbrain Astrocyte Glucodetectors and Counterregulation
• Chapter 11 Vagal Afferent Signaling and the Integration of Direct and Indirect Controls of Food Intake
• Chapter 12 Energy Metabolism and Appetite ControlSeparate Roles for Fat-Free Mass and Fat Mass in the Control of Food Intake in Humans
• Chapter 13 Pharmacotherapy for Weight Loss
• Index